Organometallic compounds oxygenation

The introduction of additional alkyl groups mostly involves the formation of a bond between a carbanion and a carbon attached to a suitable leaving group. S,.,2-reactions prevail, although radical mechanisms are also possible, especially if organometallic compounds are involved. Since many carbanions and radicals are easily oxidized by oxygen, working under inert gas is advised, until it has been shown for each specific reaction that air has no harmful effect on yields. 

By coincidence, the oxygen problem is related to our present question. In the late 18th century, molecular oxygen (02) was a revolutionary discovery for chemists because of its involvement in oxidation, and because of the demonstration that a gas reacts chemically with liquids and solids. On the other hand, nitrogen gas (N2) is, as was already known at that time, inert towards most other chemicals, in particular towards all purely organic compounds (i. e., not organometallic compounds). 

Most other organometallic compounds also react with oxygen. Aryllithium reagents have been converted to phenols by treatment with oxygen. Trialkylboranes and alkyldichloroboranes (RBCI2) can be conveniently converted to hydroperoxides by... 

The R-Hg bond is chemically stable and is not split by water or weak acids or bases. This is a reflection of the low affinity of Hg for oxygen. It can, however, be readily broken biochemically. Organomercury, like other organometallic compounds, has a strong affinity for SH-groups of proteins and peptides. 

The removal of an electron from a carbanion oxidizes it to a free radical and sometimes, in the presence of oxygen, to a peroxide. Organometallic compounds give many radical-like reactions of course, and a possible oxidation mechanism for such compounds is a preliminary dissociation into radicals followed by oxidation of the radicals and the metal. 

M. E. Minas da Piedade. Oxygen Bomb Combustion Calorimetry Principles and Applications to Organic and Organometallic Compounds. In Energetics of Stable Molecules and Reactive Intermediates, M. E. Minas da Piedade, Ed. NATO ASI Series C, Kluwer Dordrecht, 1999. 

Since dioxiranes are electrophilic oxidants, heteroatom functionalities with lone pair electrons are among the most reactive substrates towards oxidation. Among such nucleophilic heteroatom-type substrates, those that contain a nitrogen, sulfur or phosphorus atom, or a C=X functionality (where X is N or S), have been most extensively employed, mainly in view of the usefulness of the resulting oxidation products. Some less studied heteroatoms include oxygen, selenium, halogen and the metal centers in organometallic compounds. These transformations are summarized in Scheme 10. We shall present the substrate classes separately, since the heteroatom oxidation is quite substrate-dependent. 

There are many examples of organometallic compounds containing oxygen atoms as ligands an appreciable number of these resulted from reactions with O2. Early work has been reviewed by Bottomley and Sutin [ 17]. Thus we concentrate on more recent reports, and those of particular interest. 

Oxygen-Substituted Organometallic Compounds From a-Stannyl Ethers... 

Oxygen-Substituted Benzylic Organometallic Compounds From Benzyl Ethers... 

In these polymer-metal complexes of the Werner type, however, organometallic compounds are formed as reaction intermediates and/or activated complexes. As a result, the properties of polymer-metal catalysts in reductive reactions are different from those of polymer-metal catalysts in oxidative reactions. In the former, the catalytic reactions are very sensitive to moisture and air, and the complex catalysts often decompose in the presence of water and oxygen. Thus, reductive catalytic reactions are carried out under artificial conditions such as organic solvent, high pressure, and high temperature. Oxidative catalytic reactions, on the other hand, proceed under mild conditions aqueous solution, oxygen atmosphere, and room temperature. Therefore, it is to be expected that the catalytic effects of a polymer ligand will differ from the latter to the former. 

---